Fuel pump assemblies are typically used to selectively pump and/or transfer fuel from a fuel-containing tank or storage receptacle to an engine, thereby allowing the fuel to be combusted within the engine and causing the engine to perform some desired function or operation.
A fuel pump assembly is typically located within a vehicle fuel tank and normally includes an electric motor, an impeller, and a shaft which connects the electric motor to the impeller. The impeller is usually and movably housed and/or contained within a pump chamber or cavity which is formed by the cooperative engagement of a chamber cover member and a chamber body member, and which is communicatively coupled to the vehicle engine.
In operation, the electric motor selectively rotates and/or "drives" the shaft, thereby rotating the impeller. The rotating impeller "draws" and/or pumps fuel, such as gasoline or ethanol, from the fuel tank, through the fuel pump chamber, and into the vehicle engine. It is desirable to provide relatively large amounts of the fuel at a relatively high rate and/or speed in order to allow the vehicle to be selectively driven at relatively high and desirable speeds. It is further desirable to allow the fuel pump assembly to operate efficiently (e.g., without substantial losses of energy).
The rate and the speed at which the fuel is pumped into the vehicle engine can be and has been desirably increased by increasing the diameter of the impeller and increasing the size of the impeller containing pump chamber. While these modified fuel pumps have reliably pumped increased amounts of fuel at increased rates or speeds, they suffer from some undesirable drawbacks.
For example and without limitation, the pressure differential, which is created within the pump chamber by the rotating impeller, causes the impeller to undesirably contact the interior chamber forming surfaces, thereby creating significant frictional energy losses. These frictional losses decrease the overall speed of the impeller and decrease the overall efficiency of the fuel pump. Importantly, the amount of these frictional energy losses increase as the size or the diameter of the impeller is increased due the concomitant increase in the amount of the impeller surface area which operatively and frictionally contacts the interior surfaces of the chamber. Hence, increasing the size and/or the diameter of the impeller actually increases the amount of such undesirable frictional energy losses. Furthermore, the relatively large impeller tends to operatively "warp" or deform, thereby further increasing the amount of frictional contact between the impeller and the interior surfaces of the chamber and further undesirably increasing such frictional energy losses.
These prior vehicle fuel pump assemblies suffer additional energy losses due to the fluid displacement occurring at the tips or the ends of the impeller blades. In order to minimize these known "blade tip losses", the chamber body and/or cover is usually created or "machined" within very strict or "tight" tolerance limits in order to minimize the distance between the blade tips and the interior surfaces of the pump chamber. This requirement undesirably increases the manufacturing and/or production cost of these prior fuel pump assemblies and the relatively short distance between the impeller blades and the interior surfaces of the pump chamber undesirably increases the likelihood of frictional contact between the blades and the interior chamber surfaces.
There is therefore a need for an improved fuel pump assembly for use in a vehicle, which substantially reduces and/or eliminates such previously described frictional contact and "blade tip" type energy losses, and which reliably provides relatively large amounts of fuel to the vehicle engine at relatively high rates of speed.